package jisuan4h9t;

import java.util.Scanner;

public class zuobiao {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            double x1 = in.nextDouble();
            double y1 = in.nextDouble();
            double x2 = in.nextDouble();
            double y2 = in.nextDouble();
            double distance = Math.sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2)));
            System.out.printf("%.2f\r\n",distance);
        }
    }
}
